This invention relates to an apparatus for sealing cans with lids under vacuum using a vacuum chamber formed by two parts, these parts being, relative to one another, vertically movable toward and away from one another by a lifting device. The present invention relates, more particularly, to such an apparatus in which the parts can move into a closed position and apart into an open position of the vacuum chamber, a vacuum bell being mounted on one of the two parts, the bell being applicable in a gas-tight manner to the other part to enclose the vacuum chamber, the lower part being provided with a recess for the can, and a pressure plate of a sealing device, movable to a limited extent relative to the upper part being provided to press a lid on a can.
An apparatus of this kind, known from German Offenlegungsschrift (laid open patent application) No. 2,317,517 is provided with a total of three lifting devices designed as pneumatically chargeable lifting cylinders, one of which actuates a lower vacuum bell, a second actuates an upper vacuum bell, and a third actuates the pressure plate of a sealing apparatus. The operation is such that a can, provided with a lid, is placed in a lower plate-shaped recess after the lower vacuum bell has descended, after which the lower vacuum bell is moved upward and the upper vacuum bell is moved downward until the vacuum chamber is enclosed. Then the pressure plate, provided with a permanent magnet, a pneumatically acting sucker or the like, moves against the cover and then returns, leaving the lid adhering to the pressure plate. Then the vacuum chamber is evacuated, after which the lid is pressed onto the can by means of the pressure plate. Then air is admitted to the vacuum chamber again and the two vacuum bells move apart, upward and downward, respectively.
Although this known apparatus operates well in theory, it has the significant disadvantage that a considerable amount of effort is required for the three lifting devices and the switches required to control them, this effort being justified only for fully automatic apparatus having a high efficiency which operate under a continuously full load.